The Cancer Model Development Resource (CMDR) at JAX is a component of Genetic Resource Science (GRS), a group of over 100 people with broad expertise in mouse genetics and molecular biology necessary to manipulate the mouse genome. Dr. Leah Rae Donahue, Director of Genetic Resource Sciences, and Dr. Leonard Shultz, Professor, co-lead the CMDR. The CMDR provides JAX Cancer Center (JAXCC) investigators access to existing cancer models and supports development of new mouse models tailored to specific cancer research questions of importance to the Cancer Center. In turn, these models are made available to the JAXCC and wider scientific community through the GRS Repository. The CMDR provides JAXCC investigators access to mouse strains, the expertise of scientists in the Genetic Resource Science program, and project management. The GRS Repository is the largest single collection of genetically defined mouse strains anywhere in the world, and maintains an enormous variety of live strains (~1,600 at any given time), while other strains are maintained as cryopreserved stocks. To encourage use ofthe live resource, JAXCC members are supplied with mice free of charge, either as breeding pairs, small numbers of mutants and controls from mutant strains, or individual mice from strain panels. Additionally, the CMDR provides project management and genetic expertise to facilitate the development of cancer models by xenografts of human cancer samples into the NSG (NOD.Cg-Prkcdc[scid]//2rg[tm1Wji]/SzJ) mouse developed by Dr. Shultz. The CMDR advises JAXCC members who wish to develop specialized host strains tailored for particular scientific questions. Models are also developed for other research applications by combining mutant alleles to make compound mutant stocks. The CMDR and coordinates the model development process, working with the Genetic Engineering Technologies and Phenotyping Technologies resources as needed. The CMDR project manager coordinates animal care, management of biological materials, and surgical services to facilitate model development. The long-term objective is assist JAXCC members in their research by enabling the use ofthe full suite of genetic manipulation techniques and mouse model development.